1. Field of the Invention
The present invention relates to a filter element that is capable of collecting carbon dusts in a processed gas effectively and is useful as an air filter, etc. of a car, an internal combustion engine, etc.
2. Description of the Related Art
In the power source of the car, the motor bicycle, etc., it is important that sands and dusts in the suction system of the engine should be adsorbed/filtered by the filter element of the air cleaner to prevent the mixture of foreign matters into the engine, so that the engine can be caused to exhibit its function to its maximum.
In recent years, the filtering function of adsorbing and filtering the dusts, which have a wide particle size range extended from the dust with a large particle size such as a cloud of sand to the dust with a small particle size such as the carbon particle contained in the exhaust gas from the diesel car, etc. (referred to as the “carbon dust” hereinafter), is required of the filter element. Also, performances such as high cleaning efficiency, high dust holding capacity, long filtering lifetime, low intake resistance, etc. are required of the filter element at the same time.
As the filter element used at present, there may be listed the dry type filter that is formed of a filter paper, a non-woven fabric, or the like, which does not contain the oil, and the wet type filter that is formed of the filter paper or the non-woven fabric, which is impregnated with the viscous oil, for example.
As the dry type filter, in a Japanese Patent Unexamined Publication (KOKAI) Hei. 10-85539, the filter element consisting of the main filter, which is formed of the ridge-like-folded filtering member, and the pre-filter, which is arranged on the upstream side of this main filter and is formed of the non-woven fabric, are disclosed. This filter element can improve the dust holding capacity by increasing the bulk of the pre-filter. However, in the above filter element, if it is tried to implement the excellent dust holding capacity by the dry type filter, the bulk of the filter is increased even after the improved structure such as the ridge-like-folded structure, etc. to increase the adsorption area is employed. Thus, it is difficult to get the compact filter element.
In contrast, in the wet type filter, since the viscous oil on the surface of the filter can catch the dusts, the dust absorbing amount per volume of the filter can be increased, and thus reduction in size of the filter can be attained. Also, the clogging due to the dust is hard to occur and also the high cleaning efficiency can be attained. In addition, the wet type filter has such a feature that the lifetime of the wet type filter is longer than the dry type filter. However, in the wet type filter, it is known that the carbon dusts, which are caught by the oil in the filter, get out of the filter. Also, the viscous oil flows out with the flow of the gas, and thus an amount of the oil in the filter is reduced. Therefore, it is possible that, like the dust collecting mechanism of the dry type filter, reduction in the dust adsorbing capacity is caused and also the outflow oil contaminates the engine.